Golden Pass Train reservations required?

As per the info available on this site, reservations are required for the Golden Pass (Train from Lucerne to Interlaken) even if you own a Swiss Travel Pass (8 days).

However as per conversation with one of my friends who recently visited Switzerland, I am being informed that reservation is required on this line only for front seat (front view of the direction in which the train is travelling). These seats are also marked as reserved.

For the rest of the seats no reservation is required..Can some experienced people please confirm?

Is this the case with even Glacier Express and Bernina Express?

Please confirm at the earliest, since I am planning to do my bookings..